This invention relates to tool break detection of metal cutting machine tools, and more particularly to an improved electronic system and method which more clearly isolates a tool break generated electrical signal or signal change from other interfering electrical signals and changes encountered in usual metal cutting operations.
Prior tool break detection systems have utilized an interruption in a certain vibration generated electrical signal, taken from an operating cutting tool, to identify tool breakage. For example, a vibration generated electrical signal, as taken from an operating metal cutting tool, may be appropriately processed and displayed to show a characteristic spike or signal interruption upon tool breakage. Other systems may employ both low frequency and high frequency signals (as well as their mean values) in break detection analysis.
In metal cutting processes and procedures, an electrical signal which is representative of the cutting process and produced for example, by the use of an accelerometer attached to the machine, may be deleteriously affected by extraneous signals generated from normal and abnormal changes in the cutting process such as changes in the tool feed and speed, metal chip buildup, high frequency chatter, etc. These conditions may be components of the electrical signal to be processed and analyzed, and may tend to reduce the clarity and distinguishing characteristics of a spike interruption correlated to tool breakage. For example, low frequency and high frequency signals both contain important information about the cutting process and tool break events. A low frequency signal measures large scale vibrations and may be less sensitive to certain higher frequency components emanating from, for example, metal chips and their distribution as well as from tool break related phenomena. Analysis of one of such signals may lead to errors because the one signal may not contain critical tool break information. Analysis of both low frequency and high frequency signals requires more complex determinations to appraise and dismiss random noise and occurrences which may give erroneous indications of tool breakage.